Composite rocket motor cases and laminated structures which are laminates of a fiber material and a curable resin composition have been widely used in the solid propulsion industry. The development and use of nonmetallic rocket and missile motor cases and laminated structures have resulted in considerable weight reduction for these types of structures as compared with earlier materials employing high strength steel, such as heat treated 4130 steel. By reducing the motor case weight and the total weight of a rocket motor more propulsion energy per unit weight is available for delivering a rocket payload for a greater distance and at an increased velocity. With a steady improvement in high energy propellants more and more requirements have been placed on rocket motor cases and laminated structures. Therefore, a method of manufacturing composite rocket motor cases and laminated structures to yield structures having markedly superior characteristics would be well received in the solid propulsion industry to keep pace with the needs of systems employing high energy propellants such as required for advanced interceptor rocket motors.
Thus, an object of this invention is to provide a method of manufacturing composite rocket motor cases and laminated structures which have markedly superior characteristics.
A further object of this invention is to provide a method of manufacturing composite rocket motor cases and laminated structures which have markedly superior characteristics that are derived from a fabrication technique employing a layered procedure for manufacture.
Still a further object of this invention is to provide a method of fabrication wherein the superiorities of composite rocket motor cases and laminated structures are derived by a progressive addition of a tougher epoxy resin to the filament impregnating bath during the filament winding process.
Additionally, a further object of this invention is to provide composite rocket motor cases and laminated structures wherein the method of fabrication employs a resin composition composed of a high percentage of a highly-flexibilized, low-modulus resin blend for the innermost layers with a progressive increase in the toughened or hardened resin content as the filaments are wound from the innermost layers through the intervening layers to the outermost layers which are comprised of the highest-modulus resin composition.